Could you be speaking about dear Aunt Clara? The eldery Witch who wore pearls and tended to mumble as she wandered through the house, searching for other people’s Door Knobs to steal and collect. She ‘died’ on the show and in real life kind of early in the series. She was not replaced.
Marion Lorne, the actress who played Aunt Clara, had an extensive collection of doorknobs and used many of her own as props on the show.